1. Field of the Invention
The present invention relates to a motor-driven power steering apparatus.
2. Description of the Related Art
In a motor-driven power steering apparatus, as described in Japanese Patent Application Laid-open No. 6-8839 (patent document 1), an electric motor is driven by a motor driving means, a rotation of the electric motor is converted into a linear stroke of a rack shaft by a power transmission mechanism, and a wheel coupled to the rack shaft is steered and assisted.
In the electric motor used in a motor-driven power steering apparatus, some dispersion is generated in particular motors on the basis of an individual difference of each of the motors, such as in an output characteristic serving as a relation between a driving current and an output torque corresponding to the driving current, even in the same standard product. Accordingly, even in the motor-driven power steering apparatus using the electric motor having the same standard (the same specification), an output of a rack shaft is dispersed or varied, and a steering assist characteristic is dispersed or varied.
Further, even in the motor-driven power steering apparatus of the same product class, the output of the rack shaft is dispersed or varied due to a dispersion or variation of a working precision or of an assembling precision of these constituting parts, or the like. As a result, the steering assist characteristic is dispersed or varied.